Gaiten-setsu

It is the oldest systematic view of the structure of the universe in China. The first volume of the representative book on this subject, the Zhoupi Suanjing (annotated by Zhao Shuang from the end of the Eastern Han Dynasty to the Three Kingdoms period), describes the so-called First Lied-Heaven Theory, which considers the sky to be a circle and the earth to be a square, parallel plane, that the heavens move diurnally along a circular orbit centered on the North Celestial Pole, and that the radius of the sun's diurnal orbit is greatest on the winter solstice and smallest on the summer solstice. Based on the premise that the length of the shadow of an 8-foot-long hi (a measuring stick used to determine the season, direction, time, etc., held vertically on the ground. Also called a table. Equivalent to a Western gnomon) cast by the sun at noon increases by 1 inch for every 1,000 li north, the height of the sky (80,000 li) and the distance from the observation point to the celestial north pole and the sun at noon on the summer solstice are calculated by proportional calculation. It also explains that the range that the sun can illuminate is limited, and that when the sun moves away beyond this distance, it becomes night. The second volume describes the sky as a covered umbrella and the earth as an inverted bowl, with both rising in the center (north pole) (60,000 ri high) and parallel to each other at a distance of 80,000 ri, but this is thought to have been devised in opposition to the Hun Tian theory, influenced by it. An idea similar to the covered sky theory can also be found in the Indian Mount Meru philosophy.

[Kazuhiko Miyajima]

"Scientific Masterpieces 2: Chinese Astronomy and Mathematics" edited by Kiyoshi Yabuuchi, translated by Keizo Hashimoto and Hideki Kawahara (1980, Asahi Press)" ▽ "Reprint of "Essays on the History of Oriental Astronomy" by Tadaaki Noda (1989, Koseisha Kouseikaku)"

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

体系的な宇宙構造観としては中国でもっとも起源の古いもの。これについて述べた代表的な書物『周髀算経(しゅうひさんけい)』（後漢(ごかん)末から三国時代ごろの趙爽(ちょうそう)注）の巻上には、いわゆる第一次蓋天説が述べられ、天は円、地は方形の平行平面で、天体は天の北極を中心とする円軌道に沿って日周運動し、太陽の日周軌道円半径は冬至で最大、夏至で最小であると考え、南中時の太陽による、長さ8尺の髀(ひ)（季節・方位・時刻などを知るために地面に垂直に立てて用いた測定用の棒。表ともいう。西洋のノーモンにあたる）の影の長さは1000里北へ行くごとに1寸の割で長くなるとの前提から、比例計算によって、天の高さ8万里や、観測地から天の北極直下点および夏至の南中時の太陽の直下点までの距離その他を求めている。また、太陽の照らす範囲は有限で、太陽がこの距離以上遠ざかると夜になると説明する。巻下には、天は蓋笠(がいりゅう)（かさ）、地は伏せた槃(ばん)（平たい鉢）のようで、ともに中央部（北極）が盛り上がり（高さ6万里）、やはり8万里を隔てて平行をなすとする第二次蓋天説が述べられているが、これは渾天説(こんてんせつ)の影響を受け、それに対抗して案出されたと思われる。蓋天説に似た考えはインドの須弥山(しゅみせん)思想にもみられる。

［宮島一彦］

『藪内清編、橋本敬造・川原秀城訳『科学の名著2　中国天文学・数学集』（1980・朝日出版社）』▽『能田忠亮著『東洋天文学史論叢』覆刻版（1989・恒星社厚生閣）』

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